The Murúcha are the supposed mermaid race of late Irish, Scottish and Manx folklore. However their existence owes more to the imagination of modern writers and illustrators than any genuine mythological antecedence amongst the north-western Celtic peoples.

In fact most references to stereotypical representations of mermaids (or mermen) are confined to quite late Irish and Scottish folktales and can frequently be traced to foreign sources like the so-called Selkie tradition (which is largely of Scandinavian and Germanic origin. See Na Púcaí). Otherwise sea-dwelling beings are a distorted reflection of the Celtic Otherworld, the supernatural realm that lay beneath the earth and sea. As Gaelic civilization in Ireland, Scotland and the Isle of Man began to crack under the force of colonial pressures in the 16th, 17th and 18th centuries native literary traditions lost their cohesion or integrity giving rise to much that is now regarded as “genuinely” Celtic. Pookas, Kelpies, Selkies, Leprechauns and others represent this phase of Gaelic folk tradition though much of it is derived from the perception, imagination or writings of non-Gaels.